NAME

SYNOPSIS

DESCRIPTION

The
module is a simple password strength checking module for
PAM.
In addition to checking regular passwords, it offers support for
passphrases and can provide randomly generated ones.

The
module provides functionality for only one PAM management group:
password changing.
In terms of the
module-type
parameter, this is the
``password
''
feature.

The
Fn pam_chauthtok
service function may ask the user for a new password, and verify that
it meets certain minimum standards.
If the chosen password is unsatisfactory, the service function returns
PAM_AUTHTOK_ERR

The following options may be passed to the module:

min = N0 , N1 , N2 , N3 , N4

(min = disabled , 24 , 11 , 8 , 7
)

The minimum allowed password lengths for different kinds of
passwords/passphrases.
The keyword
disabled
can be used to
disallow passwords of a given kind regardless of their length.
Each subsequent number is required to be no larger than the preceding
one.

N0
is used for passwords consisting of characters from one character
class only.
The character classes are: digits, lower-case letters, upper-case
letters, and other characters.
There is also a special class for
non- ASCII
characters, which could not be classified, but are assumed to be non-digits.

N1
is used for passwords consisting of characters from two character
classes that do not meet the requirements for a passphrase.

N2
is used for passphrases.
Note that besides meeting this length requirement,
a passphrase must also consist of a sufficient number of words (see the
passphrase
option below).

N3
and
N4
are used for passwords consisting of characters from three
and four character classes, respectively.

When calculating the number of character classes, upper-case letters
used as the first character and digits used as the last character of a
password are not counted.

In addition to being sufficiently long, passwords are required to
contain enough different characters for the character classes and
the minimum length they have been checked against.

max = N

(max = 40
)
The maximum allowed password length.
This can be used to prevent users from setting passwords that may be
too long for some system services.
The value 8 is treated specially: if
max
is set to 8, passwords longer than 8 characters will not be rejected,
but will be truncated to 8 characters for the strength checks and the
user will be warned.
This is to be used with the traditional DES-based password hashes,
which truncate the password at 8 characters.

It is important that you do set
max = 8
if you are using the traditional
hashes, or some weak passwords will pass the checks.

passphrase = N

(passphrase = 3
)
The number of words required for a passphrase, or 0 to disable the
support for user-chosen passphrases.

match = N

(match = 4
)
The length of common substring required to conclude that a password is
at least partially based on information found in a character string,
or 0 to disable the substring search.
Note that the password will not be rejected once a weak substring is
found; it will instead be subjected to the usual strength requirements
with the weak substring removed.

The substring search is case-insensitive and is able to detect and
remove a common substring spelled backwards.

similar = permit | deny

(similar = deny
)

Whether a new password is allowed to be similar to the old one.
The passwords are considered to be similar when there is a sufficiently
long common substring and the new password with the substring removed
would be weak.

random = N [, only
]

(random = 42
)

The size of randomly-generated passphrases in bits (24 to 72),
or 0 to disable this feature.
Any passphrase that contains the offered randomly-generated string will be
allowed regardless of other possible restrictions.

The
only
modifier can be used to disallow user-chosen passwords.

enforce = none | users | everyone

(enforce = everyone
)

The module can be configured to warn of weak passwords only, but not
actually enforce strong passwords.
The
users
setting will enforce strong passwords for invocations by non-root users only.

non-unix

Normally,
uses
getpwnam(3)
to obtain the user's personal login information and use that during
the password strength checks.
This behavior can be disabled with the
non-unix
option.

retry = N

(retry = 3
)
The number of times the module will ask for a new password if the user
fails to provide a sufficiently strong password and enter it twice the
first time.

ask_oldauthtok [= update
]

Ask for the old password as well.
Normally,
leaves this task for subsequent modules.
With no argument, the
ask_oldauthtok
option will cause
to ask for the old password during the preliminary check phase.
If the
ask_oldauthtok
option is specified with the
update
argument,
will do that during the update phase.

check_oldauthtok

This tells
to validate the old password before giving a
new password prompt.
Normally, this task is left for subsequent modules.

The primary use for this option is when
ask_oldauthtok = update
is also specified, in which case no other module gets a chance to ask
for and validate the password.
Of course, this will only work with
UNIX
passwords.

disable_firstupper_lastdigit_check

This tells
to include upper-case letters used as the first character
and digits used as the last character of a password
when calculating the number of character classes.

use_first_pass , use_authtok

Use the new password obtained by modules stacked before
.
This disables user interaction within
.
The only difference between
use_first_pass
and
use_authtok
is that the former is incompatible with
ask_oldauthtok

oldpass_prompt_file , newpass_prompt_file = absolute-file-path

These can be used to override prompts while requesting old password
and new password, respectively.
The maximum size of the prompt files can be 4096 characters at present.
If the file size is more than 4096 characters, the output will be
truncated to 4096 characters.

SEE ALSO

AUTHORS

The
module was written for Openwall GNU/*/Linux by
An Solar Designer Aq solar at openwall.com .
This manual page, derived from the author's documentation, was written
for the
Fx Project by
ThinkSec AS and NAI Labs, the Security Research Division of Network
Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035
(``CBOSS''
)
as part of the DARPA CHATS research program.